This invention relates generally to micro-electromechanical systems (MEMS), and more specifically, to avoidance of stick-down within MEMS devices due to forces generated during operation of the MEMS devices.
Micro-electromechanical systems (MEMS) integrate electrical and mechanical components on the same substrate, for example, a silicon substrate, using microfabrication technologies. The electrical components are fabricated using integrated circuit processes, while the mechanical components are fabricated using micromachining processes that are compatible with the integrated circuit processes. This combination makes it possible to fabricate an entire system on a chip using standard manufacturing processes.
One common application of MEMS devices is in the design and manufacture of sensor devices. The mechanical portion of the sensor device provides the sensing capability, while the electrical portion of the sensor device processes the information received from the mechanical portion. One example of a MEMS device is a gyroscope. Some inertial measurement units (IMUs) incorporate one or more MEMS gyroscopes MEMS gyroscopes.
One known type of MEMS gyroscope uses vibrating elements to sense angular rate through the detection of a Coriolis acceleration. The vibrating elements are put into oscillatory motion in a drive plane, which is parallel to the substrate. Once the vibrating elements are put in motion, the gyroscope is capable of detecting angular rates induced by the substrate being rotated about an input axis. Coriolis acceleration occurs in a sense plane, which is perpendicular to both the drive plane and the input plane. The Coriolis acceleration produces a Coriolis motion having an amplitude proportional to the angular rate of the substrate.
However, due to external acceleration forces and electrostatic forces within the MEMS device, the vibrating elements sometimes become stuck to sense plates which are mounted on the substrate, affecting operation of the MEMS device. Such phenomena are sometimes referred to as xe2x80x9cstick-downxe2x80x9d.
In one aspect, a method for reducing the sticking of proof masses to sense plates in micro-electromechanical systems (MEMS) devices is provided. The method comprises determining a beginning of acceleration events, which may cause proof masses to contact sense plates, reducing sense bias voltages to the sense plates during the event, determining an end of the acceleration event, and increasing sense bias voltages to the pre-reduced levels.
In another aspect, a micro-electromechanical systems (MEMS) device is provided which comprises a substrate, and a plurality of sense plates, a plurality of motor drive combs, and a plurality of motor pickoff combs, all attached to the substrate. The MEMS device further comprises a plurality of proof masses each suspended above one of the sense plates and between one of the motor drive combs and one of the motor pickoff combs, and a control circuit configured to control a sense bias voltage applied to the sense plates based upon acceleration forces applied to the MEMS device.
In still another aspect, a control circuit for reducing stick-down within a micro-electromechanical systems (MEMS) device is provided. The control circuit comprises a processor configured to control sense bias voltages applied to the sense plates based upon acceleration forces applied to the MEMS device.
In yet another aspect, a method for suppressing stick-down of proof masses to sense plates in micro-electromechanical systems (MEMS) devices is provided. The method comprises adjusting a sense bias voltage applied to the sense plates based upon acceleration forces applied the MEMS device.
In a further aspect, a micro-electromechanical systems (MEMS) gyroscope is provided which comprises a substrate, and a plurality of sense plates, a plurality of motor drive combs, and a plurality of motor pickoff combs all attached to the substrate. The gyroscope also comprises a plurality of proof masses each suspended above one of the sense plates and between one of the motor drive combs and one of the motor pickoff combs. The gyroscope also comprises a control circuit configured to reduce or eliminate stick-down between the proof masses and the sense plates. The circuit is configured to adjust a sense bias voltage applied to the sense plates based upon an amount of acceleration applied to the MEMS device.